Extract user utility code into own module

This provides more room for expansion, and reduces the amount of
arbitrary code in the __init__.py file for the new package.

app/main/views/send.py

@@ -57,8 +57,8 @@ from app.utils import (
     get_template,
     should_skip_template_page,
     unicode_truncate,
-    user_has_permissions,
 )
+from app.utils.user import user_has_permissions
 
 letter_address_columns = [
     column.replace('_', ' ')